An Improved High-performance Open-loop V/f Control Method for Induction Machines

Scalar control has been the most popular control method implemented in induction machine drive systems. This paper presents an enhanced open-loop Volts-per-Hertz (V/f) controller aimed at strengthening the magnetizing flux of an induction machine when operated below its rated frequency. Instead of using the traditional constant V/f based on the idealized approximate steady-state machine model and/or simple stator voltage drop compensation, this method derives a new V/f ratio from a more accurate steady-state model which takes core loss into consideration as well as the stator voltage drop. In addition, a frequency boost strategy is introduced with the proposed V/f ratio for slip compensation. The analytically derived V/f ratio under different frequencies at rated load is then compared to experimentally obtained data to verify its effectiveness.